Random signal radars are radars whose transmitting signal is typically modulated by some noise source in order to generate a random transmitting signal. Because of the random properties of the signal, these radars have multiple advantages compared with conventional radars, including unambiguous measurement of range and Doppler estimations, high immunity to noise, lower detection probabilities, and advantageous ambiguity functions, among others.
For most applications, the random signal is either transmitted directly from the noise-generating source or generated digitally, then converted to analog and upconverted to carrier level. Correlation of the echo returns uses the principle that when the delayed replica of the transmitted signal is correlated with the actual target echo, the peak value of the correlation process can indicate the distance to the target. The replica of the transmitted noise, delayed, is correlated with a received signal, and strong correlation peaks are utilized to provide round trip time (RTT) estimations and ranging. This methodology generally requires a significant amount of processing and computational resources at both the transmitting and receiving ends of the system, and challenges abound. Additionally, because correlations are conducted using the delayed replica of the random transmission as a template, any ability to utilize specific phase codes more amenable to advantageous phase compressions is generally sacrificed.
Additionally in CW systems random or otherwise, leakage from a transmitted signal generally occurs due to circuit leakages, free space propagation, near field coupling, or other propagation modes. The details depend on the specific system architecture and whether single or multiple antennas are used. For close in targets, the leakage signal strength sl(t) is generally much smaller than the signal strength returned to the radar from the target, however at longer ranges or for low radar cross section targets, the received signal from the target st(t) is very weak. Since the receiver must operate when transmission is occurring, the leakage signal can still be much larger than the target return. In the absence of close-in clutter the leakage can be reduced by increasing the antenna spacing, but there is a practical limit to this. In the actual construction and operation of a radar system it is impossible to achieve zero leakage. Thus the isolation between the transmitting and receiving antennas (or channels) is often one of the limiting factors in the performance of CW radars.
It would be advantageous to provide a CW radar system which employs a randomly phase-coded system in order to realize the associated advantages while also providing the ability to recover specific phase codings more amenable to advantageous phase compressions. It would be additionally advantageous if the CW system eliminated some portion of the significant processing and computational resources associated with delayed replica correlation. It would provide additional advantage is such a system could transmit continuous wave signal in a manner greatly mitigating the impact of signal leakage.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.